Organic farmers have long touted their methods as a more eco-friendly way to nourish the world's population. But few rigorous studies have looked at the long-term costs and yields of organic farming. Now the longest and most comprehensive study to date comparing organic and conventional farming brings encouraging news for organic fans: Organic farms can be nearly as productive as regular farms for some crops, and they leave soils healthier.

A team led by agronomists Paul Mäder of the Research Institute of Organic Agriculture in Frick, Switzerland, and David Dubois of the Swiss Federal Research Station for Agroecology and Agriculture in Zürich began the 1.5-hectare trial in 1978 near Basel, Switzerland. The experiment included one group of plots that mimicked conventional farms: These were treated with chemical pesticides and herbicides and soluble nitrogen for fertilizer. For the organic plots, the team used only manure and mechanical weeding, along with plant extracts to control pests.

Over 2 decades, the average crop yield was about 20% lower in the organic plots, the team reports in the 31 May issue of Science[2]. The best-performing organic crop was winter wheat, which yielded just 10% less than the conventional harvest. Potatoes fared the worst with about 38% lower yields. The yields are impressive given that the organic plants received less than half the nutrients given to conventional plots, says John Reganold of Washington State University, Pullman. "To add that much less fertilizer and still get 80% of the conventional yields is outstanding."

Because no synthetic fertilizer had to be produced or applied, growing organic crops also required less energy than conventional crops--up to 56% less energy per unit yield. The team also found evidence that nutrient-cycling microbes are more plentiful and efficient in organic soil, making a greater percentage of nutrients available to plants. Soils also appeared to be healthier in organic plots, with 40% more roots colonized by fungi that assist with plant nutrition. Earthworms were up to three times more abundant, and there were twice as many spiders and other pest-eating arthropods.

"This study is as complete a picture as we have from anywhere," says Phil Robertson, an agricultural ecologist at Michigan State University, East Lansing. Reganold concurs: "This gives more credibility to organic systems."